Composition and method for impregnation of sheet materials with synthetic resin latices



2,760,884 ON OF SHEET Aug. 28. 1956 MATERIALS WITH SYNTHETIC RESINLATICES Filed July 22, 1954 .5633 5 5:3 2; E 35:25 25m B 35.20

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t run 2,760,884 7 COMPOSITION AND METHOD FOR IMPREGNA- TION F SHEETMATERIALS WITH SYNTHETIC RESIN LATICES George Leonard Graf, Jr.,Wilmington, Del., assignor to The C a fic C p at n, lin n, 1-,, a crpustion of Delaware f Application July 22, 1954, Serial No. 445,133Claims. (Cl. 117 65) This invention relates to a method for stiiiening afibrous sheet material,v and more particularly, it relates to a methodof preparing shoe stiffeners by treating a sheet material with asynthetic resin'latex.

High quality shoe stiffeners in the past have been made by impregnatinga flannel sheet material with finely (livided particles of cellulosenitrate. After product was stored until ready for use, at which time theimpregnated flannel was dipped into a solvent for the cellulose nitrate,applied to the appropriate shoe part and allowed to dry to a stifienedcondition.

It is also known that sheet materials such as flannel may be impregnatedby dipping the flannel into an aqueous dispersion of synthetic resin,such as a synthetic rubber latex. However in all the known processesthere are operating difliculties which arise because of the tendency ofsuch a latex to deposit in a dense impervious form. As a result of sucha formation, the porosity of the impregnated material is low and theability of the material to absorb solvents is poor. The low porosity andpoor solvent absorption prevents the achievement of the greateststifiness for a given composition of impregnated fabric. ing to knownprocesses, heavier flannels or'other supporting materials, must beimpregnated with a greater amount of resin, and such procedures arecommercially unattractive.

It has now been found that certain relatively cheap synthetic resinlatices maybe impregnated in the form-of finely divided particles into aflannel sheet material, which has a long storage life, and which maythereafter be treated with a solvent for the synthetic resin, applied tothe shoe part, and allowed .to dry and form a high quality shoestiffener. The sheet material utilized in this ingenr tion may be of thelightest grade and yet be impregr nated with a sufiicient amount ofresin to bestifiened j a very high degree, because'the present processproduces a highly porous impregnated fabric having the ability to e s bls r Perc nta e o olven tha h e eribs chiev d y t e u of syn t e n la eximprs aat ea- The attached drawing illustrates,,by means of a self.-

.explanatory flow sheet, the process of this invent on.

It is an object of this invention to providea noyel method forstifiening fibrous materials. It is another ob ject'of vthis inventionto prepare high quality shoes, 11T- ne s y using a s thet e i latex sthe m ssna in medium. It is still another object to provide a; ngle pprocess for e na n b sh et 1.1a.

wh ch a ab fbeias t f en .b sub sa s t tr atm n h r e i t il ecomeeaparentit ga the mo l explan cn'Qfi h s inysmi a .v I -abo -pbie a e.cp l hedi ac qrdanc w the process of this invention .by impregnatingasheet material with van aqueous latex containing g0 60% by weight vofvinyl polymer particles andJibQ SeQ Q}? the weight of vinyl polymerparticles 05% to 5% nondoni spers n a n which s ll le in We roomtemperature and becomes substantially insoluble, in

Therefore to obtain a desired stiffness, accord- 2,760,384 Patented Aug.28, 19,56

ice

and 0.5% to 15% of a Water-soluble polyvalent metal salt mployed as thelatex coagulant. After stripping the impregnated sheet material ofexcess liquid, the sheet mateis heated to a temperature above from about40 C tofabout 100 C., causing the dispersing agent to insolubilize andallowing the coagulant to cause the resin particles toforrn smallagglomerates dispersed through.- .out the sheet material, which as aresult of this treatment has a non-tacky, but somewhat moist surface.The renaming moisture is then removed by drying the sheet material byany known means. At any later time the dry impregnated sheet materialmay be treated with a volatile solvent for the resin agglomerates, thesheet may then be formed into the desired shape, and dried by e apora ne s P a or on of he salien the sheet material stifiens. p

In the preferred embodiment of this invention an intresnatiae med s P ab XiPsat mom .peratur ef3 parts by weight of an aqueous polystyrenelatex containing about 50% solids, 1 part of an aqueous later; of acopolymer of styrene and butadiene (in the approximate proportion of 80parts styrene to 20 parts butadiene) containing about solids, and about3% by weight of resin solids of dodecylphenyi polyg lycol eth r l r i sagent- A Fl pe eias a en h s ed;' by ht af esh; s lidscf a uminum i l te-the t m o a 1 a eous slut s. a de slowly a d wm w anc e t e i atisa toPree t 9 l z s' s la o Th P 9f t e xture t en-amu ed th a ge of 6.01.7.0 by addm ah u 1% by weight of resin solids of calcium carbonate andwater is added to provide a latex containing about"A0% solids. Thedesired sheet'materialis then dipped into the aboye mixture and strippedbetween rolls to give aloading of at least by weight of impregnatingsolids; The pregnated sheet material is then heated to about 25 G. ormore by direct contact with steam. this period he sy t t c resin P t ein h wp e lflisd shee material agglomerate to the desired and aredispersed evenly throughout the sheet material. The agglomeration occursbecause the heat causes the dispersing agent (dodecylphenyl polyglycolether in this case) to precipitate thusremoving the substance whichinhibits the tend,- ens s the r n P r i le a u te The mete? .the'n driedto remove the remaining moisture. After this treatment the impregnatedsheet material is dry and I stiifener, it is blanked into the desiredshape, treated .with

a yolatile solvent for the resin, such as methyl ethyl ketone, toluene,mixtures of these materials wi-t-h diluents, 9. th k wn Solvents, ap d ohease hih s 19 be stitfened, and the solvent is allowed to evap0rate, tl1 us producing. a stifiened sheet material. I

The following examples are given to illustrate various embodiments ofthis invention. Parts and percentages are by weight unless otherwisespecified. v Example 1.A latex blend was prepared by mixing 3 Parts I aPol styrene qus uslat x containing 5.0% resin solids and 1 part ofaqueous latex of a copolymer of styrene and butadiene in the proportionsof /20, this latex contained 45% resin solids. Into 600 grams of thislatex blend there were added'the following water at temperatures fromabout 40 C. to about '65; s

the order named: v

8.8 grams of dodecylphenyl polyglycol ether 29.2grams of 10% aqueoussolution of aluminum-sulfate 2.92'grams ofcalcium carbonate 92 grams ofdistilled Water The resulting mixture had a resin solids content of 40%and apH of 6.35.

This latex mixture was used to impregnate pieces of cotton flannelhaving a twill weave and a thickness caliper of 0.033 inch to 0.039 inchand a weight per square yard of 0.35 to 0.38 pound. A piece of thisflannel measuring 10 x 15 inches was impregnated by dipping the flannelinto the above latex mixture followed by stripping the wet materialbetween rolls placed 0.049 inch apart. The impregnated fabric was thenplaced in a chamber filled with steam at 95 C. to 100 C. in such amanner that both sides of the fabric were exposed to the steam. Afterthe fabric had been in the steam chamber for 1 minute it was removed andplaced in a circulating air oven at 110 C. for 1% hours. Of the totalweight of the impregnated fabric, 72.8% by weight was resin. This figureis called the percent resin loading hereinafter.

Two small portions, 3 x 5 inches, of the above impregnated fabric werethen tested for solvent absorption and stiffness. These pieces weredipped into a solvent comprising a mixture of 90% by weight of tolueneand by weight of a commercial petroleum naphtha fraction boiling in therange of 100 to 167 C. The two pieces, designated as A and B, were foundto have absorbed 123% and 122% by weight respectively of solvent, basedon the dry weight of the impregnated fabric before solvent treatment.

These pieces were then laminated into a simulated shoe toe portioncomprising, in the order named, shoe leather, doubler cloth, stiffener,and liner cloth. The resin migration as observed from the liner clothwas very good and there was no indication of spotty adhesion. Theadhesion between the liner and the stiffener, between the stiifener andthe doubler, and between the doubler and the leather, was good.

These laminates were then cut into strips measuring 1 x 3 inches, andtwo strips from each laminate were tested according to The StandardMethod of Testing for Stiffness in Flexure in Plastics ASTM D747-50(adopted 1950). The stiffness values for each of the two pieces(specimens 1 and 2) cut from the A laminate was 145,000 and 165,000pounds per square inch respectively giving an average of 155,000 poundsper square inch for the two pieces. The stiffness value for each of thetwo pieces (specimens 1 and 2) cut from the B laminate was 173,000 and137,000 pounds per square inch respectively giving an average value of155,000 pounds per square inch for the two pieces.

Because the thickness of the leather varied slightly from one laminateto another, the value of stifiness by the above ASTM testing method wassubject to wide variations which were believed to be due principally tothe leather thickness. Accordingly, from the data obtained from the ASTMtest there was calculated a value called rigidity which was independentof the leather thickness. This value is the inch-pounds of work requiredto deflect a one inch wide specimen with a lever arm of two inchesthrough a deflection angle of 30. The total distance through which thefree end of the specimen moved was one inch. Thus the value of rigidityis reported in terms of inch-pounds of work per inch of deflection. Therigidity of these specimens is compared with the ASTM stiflness for eachspecimen in the following table.

Rigidity ASTM (in .lbs./ Stiffness in.) (p. s. i.)

Specimen 1, Laminate A 9. 5 145,000 Specimen 2, Laminate A 11.0 165, 000Specimen 1, Laminate B 9. 7 173,000 Specimen 2, Laminate B 9. 5 137,000

Example 2.A latex blend was prepared in all reaspects similar to Example1 except the calcium carbonate was omitted and replaced with additionalwater to prepare a 40% resin solids latex. Identical pieces of flannelwere impregnated and were subjected to steam treatment and were dried inan air oven in the same manner as described in Example 1 with the singleexception that in this case the temperature of the air oven was 120 C.The percent resin loading in the impregnated fabric was 71.8%. Two smallpieces A and B were treated with solvent as described in Example 1 andwere found to have a percent solvent absorption of 130% and 129%respectively. Laminates were prepared from leather, doubler cloth,stiifener, and liner cloth as described in Example 1 and were found toexhibit good adhesion between all adjacent layers of the laminate andthe resin migration was found to be good. From each of the two pieces Aand B specimens were cut and subjected to tests to determine the ASTMstiffness and the rigidity as defined in Example 1. The followingresults were obtained:

ASTM Rigidity (in.1bS./ in.)

Specimen 2, Laminate B Example 3.A latex mixture was prepared in thesame manner as described in Example 1 with the exception that 1.25% byweight of resin solids of methyl cellulose was added as a thickeningagent and various amounts of calcium carbonate were added as a filler todetermine the effect upon solvent absorption of the impregnated fabricand thereby the effect upon its rigidity. The addition of methylcellulose is advantageous in maintaining the large amounts of filler ina dispersed condition. By increasing the filler concentration the amountof resin picked up by the fabric was decreased although the total solids(resin plus filler) remained relatively constant. The following tableshows the results obtained from the impregnation of flannel and thepreparation and testing of laminates in the same manner as described inExample 1.

Wt. Percent Solvent Absorption Percent of Calcium Carbonate Filler Basedon Weight of Resin Solids Rigidity Wt. Per- (in.-1bs./in.)

Specimen 2 Example 4.An impregnating mixture was prepared by mixing 600grams of an aqueous latex, the solid material comprising essentially acopolymer of vinyl chloride and vinylidene chloride (the latexcontaining approximately 56% resin solids and being sold commercially bythe B. F. Goodrich Company under the name Geon 351) with 9.7 grams ofdodecylphenyl polyglycol ether, 124.5 grams of a 10% aqueous aluminumsulfate solution, and 73 grams of distilled water. The resulting mixturecontained 40% resin solids.

A piece of cotton flannel weighing 0.36 pound per square yard andmeasuring about 10 inches by 17 inches was dipped into the above mixtureand stripped between rolls spaced .049 inch apart. The stripped fabricwas heated to a temperature of C. to C. by contact with steam for 1minute, and then dried in an air oven at 100 C. The dried fabric had anaverage resin loading of 73.9 weight percent.

Pieces of the impregnated fabric were then tested for solvent absorptionusing as a solvent a mixture'of 70% masses methyl ethyl ketone and 30%'cyclohexahone. "Of {four pieces tested the average solventabsorptionwas 264% by'we'ight.

In the lamination of simulated shoe toes, the resin migration was foundto 'be very good, and the adhesion between adjacent layers 'of thelaminate "was good in each case. The average ASTM stiffness was 85,500p. 's. i. and the average rigidity was 5.3 inch-pounds per inch ofdeflection measured as described in Example 1.

Example 5."In a manner similar to that described in Example 4, 600 gramsof a vinyl chloride/vinylidene chloride latex, containing about 55%solids and sold by B. F. Goodrich Company under the name of (icon 352,was mixed with grams of dodecylphenyl polyglycol ether, 151.3 grams of a10% aqueous solution of aluminum sulfate, and 69 grams of water. Theresulting mixture contained 40% resin solids.

A piece of cotton fiannel weighing 0.36 pound per square yard wasimpregnated by dipping into the above mixture and stripped between rollsspaced .049 inch apart. The stripped fabric was heated to 95 C. to 100C. by contact with steam for two minutes and then dried in an air ovenat 100 C. The dried fabric had an average resin loading of 67.2 weightpercent.

Pieces of this impregnated fabric were then tested for solventabsorption, made into a simulated shoe toe laminate, and tested forrigidity and stiffness as described in Example 4. The average solventabsorption was 169% The resin migration was very good and the adhesionbetween adjacent layers of the laminate was good in each case. Theaverage ASTM stiffness was 68,000 p. s. i. and the average rigidity was3.8 inch-pounds per inch of deflection.

Example 6.l.'n a manner similar to that described in Examples 4 and 5,600 grams of a vinyl chloride/vinylidene chloride latex containing about53% solids and sold by the B. F. Goodrich Company under the name, Geon251, was mixed with 9.7 grams of dodecylphenyl polyglycol ether, 124.5grams of a 10% aqueous solution of aluminum sulfate, and 64 grams ofwater. The resulting mixture contained 40% resin solids.

A piece of cotton flannel weighing 0.36 pound per square yard was dippedin the above mixture and stripped between rolls spaced .049" apart. Thestripped fabric was then heated at 95 C. to 100 C. by contact with steamfor 2 minutes and then dried in an air oven at 807 C. The dried fabrichad an average resin loading of 75.2 weight percent.

Pieces of this impregnated fabric were then heated for solventabsorption, made into a simulated shoe toe laminate, and tested for ASTMstiffness and rigidity by the methods described in Example 4. Theaverage solvent absorption was 125%. The resin migration in the shoe toelaminate was good and the adhesion between adjacent layers of thelaminate was good in each case. The average ASTM stiffness was 82,000 p.s. i. The average rigidity was 3.9 inch-pounds per inch of deflection.

Example 7.For comparative purposes, similar pieces of flannel wereimpregnated by three different processes. The first two methods areknown to the public and the third method is identical with thatdescribed in Example I. In each case, the techniques used were intendedto produce the highest quality shoe stifl ener possible withtheparticular ingredients used.

In the first method the impregnating medium was a solution of cellulosenitrate. In the second method the impregnating medium was a' mixture of3 parts of aqueous polystyrene latex and 1 part of an aqueous latex ofan 80/20 copolymer of styrene/butadiene and 1% by weight of resin solidsof an organic phosphate saltsold by Victor Chemical Works under the nameof Victor Stabilizer-53. The total resin solids content amountedeasilyby the latex. In the third-methodathermosensitive 6 latexim'pregn'atiiin identical with that described in example lwas utilized.p

In each case identical pieces of'cottonflannel weighing 0.36 pound persquare yard were impregnated, made into simulated shoe toes, and weretested according to erican Standards Assoc. Bulletin on Mars SafetyShoes No. Z4l.ll944. The values-obtained were reported as a CompressionNumber which is the total number of pounds required to depress the shoetoe to a distance of 0.5 inch from the insole. Thus higher CompressionNumbers are equivalent to a greater -de'gree of stiffness. The laminatemade from the cellulose nitrate impregnated shoe stiffener, called thefirst methodabove, had a Compression Number of 31. The laminate preparedwith a stiffener made by 'the'secorfd method above had a CompressionNumber of 51. The laminate made by the process of this invention,called'the third method above, had a Compression Number'of 95.Furthermore, laminates prepared by the third method above, utilizingvery light flannel, 0.121 pound per square yard, had a CompressionNumber of 48, illustrating that :a higher degree of stiffness canbeachieved bythe process off the present invention even when utilizing'flannelof one-third the weight required to produce the same stiffness.by the known cellulose nitrate process.

Any of several kinds of synthetic resins having eleci trostaticproperties may be used as the major ingredient in the impregnatinglatex, although the vinyl resins are preferred, such as polystyrene,polymethyl styrene, polyvinylhalides, polyvinylidene halides,polyacrylates, .poly-' acrylonitrile, and 'polyallcylacrylates. It isdesirable in many instances to employ .a plasticized resin, such as a.mixture of polystyrene and a copolymer of high styrene content and lowbutadiene content, the. copolymer acting as a plasticizer and therebycausing the polystyreneito be; less brittle although retaining itsstiffness.- Other known plasticizers such as organic esters, and othernon-volatile; non-hardening liquids-may be incorporated with the baseresin to reduce brittleness in the same manner as the styrene/butadienecopolymer is used above. of styrene or of vinyl halides are particularlydesirable because of their availability and low cost; 7

Many varieties of resins and; combinations of polymers have been foundto be useful in this process. One useful group of resins is a copolymerof styrene/butadiene containing 4% to 20% by weight of butadiene. Apreferred formulation is a mixture of 3 parts polystyrene with 1 part ofan 20 copolymer of styrene/butadiene; which mixture has a totalcomposition of styrene and 5% butadiene. The proportions of polystyreneand the styrene/butadiene copolymercan be varied within the general:range of 420% by weight of butadiene'zin the total mixture to produceslightly stiffer and harder compositions as the butadiene proportion isreduced and softer more elastic compositions as the butadiene proportionis increased; The same variety of compositions can be obtained by mixingwellrknown plasticizers with polystyrene or other hard plasticmaterials, particularly the vinyl polymers such as vinyl halide,vinylidene halide; alkyl acrylates, and other resins known to thoseskilled in'the art. a

The latexused as a starting material in the prepara tion of theimpregnating bath ofthis inventionis a colloidal dispersion of one ormore of the above resins in an aqueous medium; Preferably, thedispersion contains from about 40% to about 60% resin solids, while th'eremainder is essentially all water. These dispersions-or, latices areavailable commercially on the open market in concentrations of 40% to60% solids, or they maybe prepared by known methods, such asvdispersionpolw meri'zation. The latex of resin andwater constitutes thelargest portion of theirnpr'egnating mixture of this in; vention' andthe additives described below constitute less; than" abbut .l5%' of thetotal weight of the impregna mixture, although there are someembodiments of this Polymers invention wherein a large amount of filleris employed.

After all additives are incorporated into the latex, it may then bediluted if desired, and in any case will contain about 20% to 60% resinsolids in the final form as an impregnating bath.

,Dispersing agents are required additives to the latex utilized in thisinvention so as to stabilize the latex against premature coagulation.The dispersing agent is non-ionic and must be one which is soluble inthe latex medium at room temperature and increasingly insoluble athigher temperatures. The solubility of these substances should be suchthat it is soluble in water at some temperature from about roomtemperature (20 C.) to about 40 C. and that the substance is insolublein water at some temperature from about 40 C. to about 100 C. Of course,the solubility of chemical substances normally changes rather slowlywith temperature and it is not intended to limit this invention to thosedispersing agents which are completely soluble at room temperature andcompletely insoluble at 40 C., but rather to include those non-ionicdispersing agents which can be dissolved in an aqueous medium at roomtemperatures or thereabout and which have inverse solubilitycharacteristics and will therefore become insoluble as the temperatureis increased up to about 100 C. The solubility requirement of thedispersing agents used in this invention is such that the impregnatinglatex may be prepared at ordinary temperatures (20 C. to 40 C.) and thedispersing agent will be soluble and thus prevent any gross coagulationor premature agglomeration of the latex but as the temperature is raisedto some convenient point (40 C. to 100 C.)

the dispersing agent becomes insoluble and allows agglomeration tooccur. The preferred compounds which function as non-ionic dispersingagents and have inverse solubility characteristics include thepolyglycol ethers such as octylphenyl polyglycol ether, dodecylphenylpolyglycol ether, and ethers formed as the condensation product ofethylene oxide and rosin. The alkylphenyl polyglycol ethers arepreferred in this invention.

The amount of dispersing agent employed is at least about 0.5 andnormally not more than by weight of the resin solids present in thelatex. If the liquid latex constitutes about 20% to about 60% resinsolids, then the dispersing agent will be present from about 0.1% toabout 3.0% by weight of the total latex. Greater amounts than 5% byweight of the resin solids may be used without affecting the processother than increasing the costs involved. Generally, about 3% ofdispersing agent is recommended for the preferred embodiments of thisinvention since this amount effectively inhibits coagulation oragglomeration of the latex at room temperature as well as reducing thesurface tension of the latex liquid and thus permit rapid penetration ofthe latex into the sheet material.

Coagulants which may be employed in the process of this invention arethe water-soluble polyvalent metal salts which may be chlorides,nitrates, sulfates, acetates, etc. of aluminum, magnesium, calcium,iron, tin, copper, cobalt, chromium, cadmium, strontium, etc. Of thesevarious salts calcium chloride, ferric sulfate, magnesium sulfate, andaluminum sulfate are desirable, although the latter two are preferredbecause of their lower costs, better solubility characteristics, and thefact that they do not impart undesirable color to the finished product.The alums such as the potassium, sodium, or ammonium aluminum sulfatesare as desirable as aluminum sulfate as the coagulant in this process.

The amount of coagulant required will vary slightly with the chemicalnature of the coagulant salt, the type and amount of resin employed, andother reaction conditions. For the preferred coagulant, aluminumsulfate, approximately 0.5% by weight of the resin solids present in thelatex is suflicient to accomplish the desired result, although in thepreferred embodiment of this invention about 1% is normally employed.For other coagulants, some of which are known to be less active and lesseflicient than aluminum sulfate, the amount employed may be as high as10% or 15% by weight of the resin solids. There may be other variablesof this process which will affect the amount of coagulant required toachieve the most eflicient operation; these variables including thetemperature employed to insolubilize the dispersing agent, the chemicalnature of the impregnating medium, and other factors known to thoseskilled in the art, and it is therefore intended to include otherconcentrations of coagulant in this invention since it is not a criticalfeature thereof and is generally well understood by those skilled in theart.

The coagulant salts of this invention are capable of causing thecolloidal resin particles in the latex to change into a dense curdlikemass if there is no protective effect of a dispersing agent. A changeinto such a dense curdlike mass is referred to herein as coagulation. Inthe process of this invention the colloidal resin particles of the latexare protected from the action of the coagulant salt by the presence of adispersing agent which gradually becomes insoluble as the temperature ofthe latex'is raised. As the dispersing agent becomes insoluble the resinparticles form small clusters of the original colloidal particles andthese clusters deposit in the impregnated material in the form of aporous mass as distinguished from the coagulated, dense curdlike massreferred to above. The formation of the porous clusters is referred toherein as agglomeration.

The material which is to be stiffened may, in general, be any fibroussheet material such as any of the varieties of fabrics, textiles, feltedmaterials, mats, papers, or the like. The sheet material may be made ofnatural or synthetic fibers or a mixture of the two. In the case of shoestirfeners the material commonly employed is a cotton flannel, althoughnon-woven sheet material or even paper may be used in some cases.

Filler materials may be incorporated into the impregnating medium ofthis invention to serve several useful purposes. For example, the fillermay be used to reduce the cost of the materials used in the impregnatingbath. The use of a filler in many instances causes the impregnatedmaterial to be more porous and therefore to be able to absorb moresolvent and achieve a greater stifiness. In some cases, the use of afiller enhances the adhesiveness of the impregnated material to anadjacent laminating layer. Some filler materials serve many purposes inaddition to their diluent elfect, for example, they may act as abuffering agent as will be explained later, they may improve fireresistance, improve adhesiveness and solvent absorption and other usesapparent to those skilled in the art. In the manufacture of shoe partsusing the impregnated shoe stiffner of this invention it has been foundthat the incorporation of filler material permits the shoestifiener tobe handled easily when it is wet with solvent and ready to beincorporated into the shoe part and, furthermore, after the shoe parthas been assembled there is less likelihood that resin solids willmigrate from the shoe stiffener and cause visible spotting on theleather surfaces of the shoes. Filler materials which may be usedinclude water insoluble salts such as calcium carbonate and calciumsulfate, infusorial earths, bentonite clays, and other inert materialsknown to those skilled in the art. The amount of filler material whichmay be used may be as much as about by weight of the resin solidspresent and a range of values of about 20% to 50% is preferable for mostembodiments of this invention.

Thickeners have utility in this invention when it is desired toimpregnate a fabric with greater and greater amounts of resin solids,and when fillers and other ingredients of the latex have a tendency tosettle out. Thickeners which have been used successfully include methylcellulose and methyl carboxy cellulose. Other equally useful thickenersare well known to those skilled in the art.

In the preparation of high quality shoe stiifeners and in certain otherembodiments of this invention it is highly desirable to adjust the pH ofthe impregnating latex so that there will be no injury to the supportingfibrous sheet material due to acidic attack. Latices containing amixture of polystyrene and a copolymer of styrene/butadiene, adispersing agent, and a coagulant salt as described above have beenfound to have a pH of 3.5 to 4.5, and, because of such acidity, todamage the flannel impregnated by such latices. It is thereforepreferable to add a buffer material to adjust the pH to a value of 6.0to 7.0. Any of a large variety of salts may be added to the latex toperform the buffering function, such as the alkali metal and alkalineearth metal carbonates, bicarbonates and hydroxides. Calcium carbonatehas been found to be desirable for this purpose, and approximately 1% byweight of the resin solids is sufi'icient to raise the pH to 6.0 or 7.0.It is also possible to utilize hydroxides, such as calcium hydroxide, invery small amounts to adjust the pH to the desired level of 6.0 to 7.0.

As a final step in the preparation of the impregnating latex, water maybe added to form the desired concentration of resin solids, which formost embodiments of this invention will be from about 20% to about 60%by weight of solids. For the preparation of most shoe stifieners, aconcentration of about 40% solids has been found to be preferable.

Because of the sensitivity of synthetic resin latices towardcoagulation, it is recommended that the impregnating composition beprepared by mixing the ingredients in a specific order; namely, that theresin latex and the dispersing agent be, thoroughly mixed before addingthe coagulant. Furthermore, it is helpful to add the coagulant slowly,and in a diluted condition, to the latex while the latex is beingagitated. Such precautions as these assist in preventing any localizedcoagulation of the resin solids in the latex. It may be desirable insome embodiments of this invention to employ a stepwise process in whichthe coagulant is in a bath separate from the latex bath, and the clothwhich is to be impregnated is contacted with one bath containing thelatex particles and a second bath containing the coagulant.

In the process of preparing a stiffened material such as a shoestiffener, cotton flannel or other supporting sheet material is dipped,sprayed, covered, or otherwise treated with the impregnating latex,which is prepared according to the above description.

The excess liquid is removed from the wet impregnated material by asuitable means such as coacting stripping rolls, a wiper knife, or thelike. Such an operation is capable of loading the supporting material tothe desired amount of about 50% or more by weight of impregnating solidsif the original impregnating latex contains about 40% solids. Some shoestiffeners are prepared with much less than 50% resin solids and thisprocess is capable of preparing such shoe stilfeners by loading thematerial with less than 50% solids. The stripped, impregnated materialis then heated to cause agglomeration of the resin solids and toevaporate the remaining water from the material. Any method of heatingmay be utilized although it has been found that the most desirableresults are obtained if the material is heated in a humid atmosphere,for example, 95 C. by contact with steam at about 95 C. to about 120 C.The steam treatment is followed by drying to produce a dry, impregnatedmaterial having better solvent absorption characteristics, and thereby,a greater stiffness, than can be produced by using other methods. Insome cases it may be desirable to subject the dried impregnated sheetmaterial to the action of calendering rolls to produce an accuratecaliper thickness in the material.

The dried impregnated material, by the above treatment, contains smallagglomerates of resin particles uniformly dispersed throughout the sheetmaterial. As such this material may be stored if desired, or it may beused in the production of a stiffened article of manufacture, such as abox toe or counter in a shoe, a laminate with other materials, shapedmolds, and other similar objects. The stiffening process is accomplishedby treating the dry, impregnated material with a solvent for the resin,forming the solvent-treated material into the desired shape and allowingthe solvent to evaporate leaving a stiff, self-supporting, article. Thesolvent for the poly" styrene resin may be methyl ethyl ketone, toluene,or mixtures of these materials,and the solvent for the polyvinylchloride resin may be methyl ethyl ketone, cyclohexanone, or mixtures ofthese materials with each other or with diluents. Other solvents forthese and other operable resins are known to those skilled in the art.

The process of this invention is particularly useful in the preparationof shoe stiffening materials such asbox toe or shoe counters and it alsofinds a wide variety of uses in the preparation of impregnated materialswhich are used to stilfen or otherwise strengthen materials with whichit is laminated. The impregnated material of this invention may be usedto repair sheet metal articles such as roof gutters, downspouts, fendersand bodies of automobiles. This material also finds use in covering thedecks and hulls of small boats, in the preparation of artificial limbs,in the manufacture of mannikins, and various display devices and in anyof a variety of laminating applications.

I claim:

l. A process for preparing sheet materials cap-able of being stiffenedconsisting essentially of preparing an aqueous latex containing (1) 20%to 60% by weight of a vinyl polymer, (2) 0.5% to 5% by weight of said:vinyl polymer of a non-ionic dispersing agent which is soluble in waterat some temperature from about room temperature to about 40 C. and issubstantially insoluble in water at some temperature from about 40 C. toabout 100 C., and (3) from about 0.5% to about 15% by weight of saidvinyl polymer of a water-soluble polyvalent metal salt; impregnating afibrous sheet material with said aqueous latex, removing excess latexfrom said sheet material, heating said sheet material at a temperatureof 40 C. to 100 C. until the liquid latex particles agglomerate, andthereafter drying the sheet material.

2. The process of claim 1 in which the heating of said sheet material ata temperature of 40 C. to 100 C. is accomplished in a humid atmosphere.

3. A process for preparing sheet materials capable of being stiffenedconsisting essentially of preparing an aqueous latex containing (1) 20%to 60% by weight of a mixture of a major portion of polystyrene and aminor portion of a copolymer of styrene/butadiene, (2) 0.5% to 5% byweight of said vinyl polymer of a nonionic dispersing agent which issoluble in water at some temperature from about room temperature toabout 40 C., and insoluble in water at some temperature from about 40 C.to 100 C., and (3) from about 0.5% to about 15% by weight of said vinylpolymer of a watersoluble polyvalent metal salt; impregnating a fibroussheet material with said aqueous latex, removing excess latex from saidsheet material, heating said sheet material to a temperature of at least95 C. by direct contact with steam until the liquid latex particlesagglomerate, and thereafter drying the sheet material.

4. The process of claim 3 in which the weight ratio of said majorportion to said minor portion is about 3:1 and said copolymer containsstyrene and butadiene in the Weight ratio of about :20.

5. The process of claim 4 in which said polyvalent metal salt isaluminum sulfate.

6. The process for preparing a shoe stiffener consisting essentially ofpreparing an aqueous latex containing (1) 30% to 50% by weight of resinsolids comprising 3 parts by weight of polystyrene and 1 part by weightof an 80/20 copolymer of styrene/butadiene, (2) 0.5% to by weight ofsaid resin solids of an alkyl phenyl polyglycol ether dispersing agent,(3) about 1% of aluminum sulfate, and (4) adding suflicient bufiermaterial to adjust the pH of said latex to a value of about 6.0 to 7.0;impregnating a cotton flannel sheet material with said aqueous latex,removing excess latex from said sheet material until at least 50% of theweight of the impregnated sheet material comprises latex solids, heatingsaid sheet material to a temperature of 95 C. to 120 C. in a humidatmosphere until the liquid latex particles agglomerate, removing theremaining moisture in said sheet material, and recovering a dr flexible,impregnated fiannel sheet material capable of being stiffened bysubjecting it to the action of a solvent for said resin solids.

7. The process for preparing a shoe stiffener consistw ing essentiallyof preparing an aqueous latex containing 1) 30% to 50% by weight ofresin solids comprising 3 parts by weight of polystyrene and 1 part byweight of an 80/20 copolymer of styrene/butadiene, (2) 0.5% to 5% byweight of said resin solids of an alkyl phenyl polyglycol etherdispersing agent, (3) about 1% of aluminum sulfate, and (4) 20% to 50%by Weight of said resin solids of calcium carbonate; impregnating acotton flannel sheet material with said aqueous latex, removing excesslatex from said sheet material until at least 50% of the weight of theimpregnated sheet material comprises latex solids, agglomerating theliquid latex particles in the resulting sheet material by heating saidsheet material to a temperature of 95 C. to 120 C. by direct contactwith steam, removing the remaining moisture in said sheet material, andrecovering a dry, flexible, impregnated flannel sheet material capableof being stiffened. by subjecting it to the action of a solvent for saidresin solids.

8. The process for preparing a shoe stiffener consisting essentially ofpreparing an aqueous latex containing (1) 30% to 50% by weight of resinsolids comprising 3 parts by weight of polystyrene and 1 part by Weightof an 80/20 copolymer of styrene/butadiene, (2) 0.5 to 5% by weight ofsaid resin solids of an alkylphenyl polyglycol ether dispersing agent,(3) about 1% of aluminum sulfate, and (4) 20% to by weight of said resinsolids of calcium carbonate, impregnating a cotton flannel sheetmaterial with said aqueous latex, removing excess latex from said sheetmaterial unit at least 50% of the weight of the impregnated sheetmaterial comprises latex solids, agglomerating the liquid latexparticles in the resulting sheet material by heating said sheet materialto a temperature of 95 C. to 120 C. by direct contact with steam,removing the remaining moisture in said sheet material, and recovering adry, flexible, impregnated flannel sheet material capable of beingstifiened by subjecting it to the action of a solvent for said resinsolids.

9. A liquid composition consisting essentially of (1) 20% to by weightof a vinyl polymer, (2) 0.5% to 5.0% by weight of said vinyl polymer ofa non-ionic dispersing agent which is soluble in water at sometemperature from about room temperature to about 40 C. and is insolublein Water at some temperature from about 40 C. to about 100 C., (3) 0.5%to 15% by weight of said vinyl polymer of a water-soluble polyvalentmetal salt, and (4) suflicient water such that the sum of all componentsequals 100%.

10. A liquid composition consisting essentially of (1) 20% to 60% byweight of colloidal resinous particles of polymeric styrene andpolymeric butadiene in the proportions of 4% to 20% by weight ofpolymeric butadiene and 96% to by weight of polymeric styrene, (2) 0.5to 5.0% by weight of said resinous particles of an alkylphenylpolyglycol ether dispersing agent, (3) about 1% by weight of saidresinous particles of aluminum sulfate, (4) 20% to 50% by weight of saidresinous particles of calcium carbonate, and (5) sufficient water suchthat the sum of all components equals 100%.

References Cited in the file of this patent UNITED STATES PATENTS

1. A PROCESS FOR PREPARING SHEET MATERIALS CAPABLE OF BEING STIFFENEDCONSISTING ESSENTIALLY OF PREPARING AN AQUEOUS LATEX CONTAINING (1) 20%TO 60% BY WEIGHT OF A VINYL POLYMER, (2) 0.5% TO 5% BY WEIGHT OF SAIDVINYL POLYMER OF A NON-IONIC DISPERSING AGENT WHICH IS SOLUBLE IN WATERAT SOME TEMPERATURE FROM ABOUT ROOM TEMPERATURE TO ABOUT 40* C. AND ISSUBSTANTIALLY INSOLUBLE IN WATER AT SOME TEMPERATURE FROM ABOUT 40* C.TO ABOUT 100* C., AND (3) FROM ABOUT 0.5% TO ABOUT 15% BY WEIGHT OF SAIDVINYL POLYMER OF A WATER-SOLUBLE POLYVALENT METAL SALT; IMPREGNATING AFIBROUS SHEET MATERIAL WITH SAID AQUEOUS LATEX, REMOVING EXCESS LATEXFROM SAID SHEET MATERIAL, HEATING SAID SHEET MATERIAL AT A TEMPERATURE40*C. TO 100*C. UNTIL THE LIQUID LATEX PARTICLES AGGLOMERATE, ANDTHEREAFTER DRYING THE SHEET MATERIAL.